Resistor



L. L'. JONES Jan. 23, 1934.

RESISTOR Filed Jan. 25, 1930 INVENTOR Lesfer L. Jones Patented Jan. 23, 1934 UNITED STATES PATENT! OFFICE 10 Claims.

This invention relates to resistors, and more particularly to the manufacture of variable high resistors.

In my Patent No. 1,593,658, issued July 27, 1926, I have disclosed a variable high resistor in which the desired high resistance is obtained by using a resistance surface or film pressed into contact with a wire wound element, the windings of which are severed to conductively disconnect them from one another, while variation of the high resistance value is obtained by means of a movable contact sliding over the wire wound element. The objects of the present invention are, generally, to improve such resistance units in order to make possible a desired gradual resistance variation and smoothness of operation; to improve the method of manufacturing this type of resistance unit; and to devise a method of manufacture of the resistance unit which will permit of the manufacture of the previously mentioned improved resistance unit.

In cutting or severing the windings of the wire wound contactor element it is important to avoid burring or abrading of the severed ends of the windings in order to prevent them from being brought into contact with one another. In ac cordance with the present invention, the windings are cut by forcing a cutting edge against the windings transversely of the plane thereof, that is to say, the windings are each cut by movement in parallel directions so that there is no tendency for the severed ends to be brought into contact with neighboring severed ends.

One of the difficulties which arises with the type of resistance unit now under discussion is to prevent movement of the windings, particularly after they have been severed. In accordance with a further feature of the present invention, the windings are cut by forcing a relatively blunt cutting edge against the windings in order to indent the ends severed thereby into the insulation core about which they have been wound. This imbedding of the windings protects them from being dislodged by externally applied friction and helps anchor the individual windings in place.

In order to obtain the desired increased smoothness of operation and gradualness of resistance variation it is desirable to increase the fineness of the wire windings and to decrease the spacing thereof. This, however, weakens the inr dividual turns of wire and thereby reduces their resistance to movement. This fact, taken together with the increased nearness of the adjacent windings, makes it difficult to avoid accldental contact and short circuiting between windings. In accordance with the method of the present invention the windings are made of contact wire so fine as will permit of the desired gradual resistance variation and desired smoothness of operation, but these windings are bound in position before being cut, and the cutting is performed as previously outlined, that is, by forcing a relatively blunt cutting edge against the windings in order to cut them in parallel directions and in order to indent the ends of the windings.

In accordance with a further feature of my invention, this binding of the windings before cutting thereof is performed by pressing the windings permanently into intimate contact with the high resistance surface exactly as these elements are to remain and be used in the finished resistor, and thereafter cutting the windings. In this manner there is no subsequent operation which will tend to displace the severed windings with consequent short circuiting therebetween.

The preferred form of resistor is one in which the resistance surface and contact windings are arranged in annular fashion so that contact therewith may be made by a rotatable contact arm. For the manufacture of such a resistor it is merely necessary to wind an insulation strip with the fine contact wire, and thereafter bend the same into the desired arcuate configuration. The high resistance surface and the wire wound contact element are pressed into intimate and binding contact in the desired arcuate shape, and thereafter the wire windings are out along an edge of the insulation strip preferably by forcing a tool having a similar arcuate cutting edge against the windings.

Still another object of my invention resides in the provision of a suitable cutting punch or tool for use in the practice of the present invention.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the method and the apparatus and their relation one to the other as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by drawing in which:

Fig. 1 is a section taken through a partially completed resistance unit during the cutting therof; and

Fig. 2 is a plan view of a finished resistance unit.

Referring to the drawing, the resistor consists, generally, of a high resistance element or surface A, a severed wire wound contact ele-- ment B, and a movable contact 0 (in Fig. 2) engaging the wire wound element B. With this arrangement it is obvious that all of the advantages of a painted or coated resistance film or surface, such as the possibil of attaining any desired high resistance and su able taper 15.; thereof, are retained, and meanwhile the d d vantages thereof, such as change in resistance value due to abrasion by a contact element, are obviated. Similarly, the advantages of a wire wound resistance element, such as the conven ience and durability of the sliding contact obtainable, are retained, but the disadvantages, such as the impossibility of obtaining extremely high resistance value, are obviated.

In accordance with the present invention, a very gradual and very smooth variation of resistance value is made possible by winding the wire wound element B of very many closely spaced turns of fine wire. In this respect the drawing does not do the resistance unit justice because the windings have been drawn relatively coarsely in order to illustrate the same with greater clarity. The fine wire employed is entirely too Weak to make the windings selfsupporting after they have been severed, and, accordingly, they are bound in place before being severed, and this is preferably accomplished by the method and with the structure next described.

The outer periphery of the finished resistor consists of a ring or short length of bake tubing 12. This ring acts as a clamp ring for "at." ing an outward pressure and therefore must be strong in tension, and it is for this reason that the ring is preferably made of bakelite. The center body of the resistance unit consists of an insulation member 14 which acts as a wedge block and is subjected to compression. This member may therefore be made of molded in sulation which would be unsuitable for the clamp ring 12, and which is finished because it permits of the provision of suitable mounting apertures 16, a spindle aperture 18, and mounting bosses 20. The periphery of the molded wedge block 14 is tapered or conical in configuration.

To make the resistance element A a thin ficxible strip of insulation 22 is painted or other wise coated with a film of resistance material 24, a plurality of coatings being applied if a tapered resistance value is desired. The contact element B is made by winding a relatively thin and flexible strip of insulation with a continuous wire winding 28. The resulting resistance and contact elements are bent into arcuate configuration, inserted within the clamp ring 12, and pressed into intimate contact with one another by forcing the wedge block 14 inside of the wire wound element B. A strip of relatively soft material is preferably placed between the resist ance element A and the clamping ring 12 to act as a soft backing sheet, indicated at 30, for the resistance element. It will thus be clear that the wire wound element B is handled and manipulated while the windings are unsevered, and these windings are pressed into intimate contact with the resistance element A, and are bound permanently in place exactly as they will remain in the finished resistor.

The windings are next out. For this purpose I have devised a special cutting tool or punch D. This consists of an annular cutting edge 32 so that the punch may be forced against the windings transversely of the plane thereof, so that the windings are cut in parallel directions, and there is no tendency for the ends severed by the tool D to be buried or abraded into contact with one another. Furthermore, the cutting edge 32 preferably made relatively blunt in order to indent the ends of the windings severed thereby into the insulation strip 26, thereby protecting these windings from being opened by friction across the severed surface, and further to help loci; the severed windings in place around the periphery of the contact clement B. For this purpose it is desirable that the cutting edge be tapered on both sides, that is, both internally and externally, and that these sides be arranged symmetrically with respect to the direction of movement of the punch. A taper of 20 degrees, that is, a cutting edge having a total angle of 46 degrees, has been. found very satisfactory for attaining the desired result.

While I have referred to the cutting edge being relatively blunt and shall so refer thereto in some of the claims, I do not mean to imply that the cutting edge itself is dull or edgeless, but rather merely that the sides of the cutting edge are properly tapered or shaped to obtain the desired indentation of the severed ends of the windings. For example, in the illust ated punch the cutting edge keen and sharp is obtainable with a 40 degree tool. Furthermore, it is possible to make the cutting edge itself of ti; e tool have a much more acute angle and to immediately follow the edge with sloping sides appropriate for the desired indenting function, the indentation in such case immediately following instead of coinciding with the cutting act on In the appended claims I intend the expre on relatively bit 0 cutting edge to mean merely the edge is properly shaped to indent the severed ends.

It should further be noted that the cut" punch D may very conveniently be provided with a guide pin 34 which may be formed integrally with the punch and which is located centrally of the annular cutting edge 32. With this construction the cutting punch. may be located prop- 'erly simply by inserting the guide in in the aperture 18, which aperture is s quently to be used for receiving the conventional bushing and contact arm spindle.

It should be noted that the windings are severed on the back of the unit, that is, the side opposite the contact arm C in the finished unit, and the side facing the panel or base upon which the unit is to be mounted. The opposite edge of the coin tact element B projects beyond the c amp r ng and the wedge block 14, thereby facili ating con-- tact therewith by the rotatable contact a m 0. As is best indicated in the finished tor may be provided with an insulation stop or block 36 for limiting the movement of the contact arm C in either direction, and three terminals or connecting lugs, 33, 40, and 42, may be provided, the terminals 38 and 42 being connected with the ends of the contact element B, and the terminal i0 being connected to the bushing or otherwise con nected with the contact arm C. The arrangement as shown is suitable for use either as a resistor or as a potentiometer, and it obvious that if the unit is not intended to be used as a potentiometer one of the terminals 33 or 42 may be omitted.

The resistance and contact elements are preferably made separate, like the resistance element A and contact element B disclosed, because this makes it possible for the resistance film 2% to be coated on a very thin insulation strip 22 which may subsequently be bent into the desired circushape without cracking, stretching, or breaking the continuity of the resistance film. Furthermore, the manufacturer may prepare and keep in stock standard parts for the resistance unit, the resistance element A only being changed to fit the particular requirements in any case. Also, the resistance surface is not damaged by any other manufacturing operations, such as the tight winding of the contact element B, and is subjected to no friction except the pressing thereagainst or" the contact element when the resistor is assembled, and this initial conditon is permanently retained.

lhe method of the present invention makes it possible to use exceedingly fine wire and to wind the same very closely. In one specific commercial unit in which the contact element B has a diameter of about one and a quarter inches, the practice of my invention has made it possible to change from a former maximum of 155 contacts between zero and maximum resistance to a total of 430 or more contacts. A winding of 100 turns to the linear inch is readily made commercially practicale when the method here disclosed is followed. This improved winding results in increased. smoothness of operation and more even variation of voltage, as well as a more gradual resistance curve. Meanwhile, the advantages of absolute freedom from resistance variations due to wear on the resistance element, low seliTinductance, and certain and positive contact, are all retained.

To summarize, the practice of the present invention makes it possible to so sever the windings that the ends thereof will not be b .rred or abraded or displaced into contact with one an other. Meanwhile, the cutting operation may itself be used to imbed the cut ends of the windings into the insulation core about which they have been wound. The use of exceedingly fine wire is made possible by binding the wire in place before cutting the turns thereof, and they are preferably bound place while being pressed into intimate contact with the high resistance element. In the case of a circular unit these steps are preferably performed while keeping the resistance and contact elements in the desired arcuate shape and only after they have been permanently located in position in the actual resistance unit or the windings cut. The cutting operation is made simple and inexpensive by the use of a special cutting punch having an annular cutting edge with an advantageous taper, and having appropriately located guide means.

It will be apparent that while I have shown and described my invention in the preferred form, many changes and modifications may be made in the method and structure disclosed without departin from the spirit of the invention, defined in the following claims.

I claim:

1. In the manufacture of variable high resistances comprising a resistance surface, and severed wire windings in contact therewith, the method which includes simultaneously cutting all of the windings by forcing a cutting edge lying in a plane parallel to the plane of the windings against the windings in a direction transversely of the plane thereof, in order to prevent the ends severed thereby from being burred or abraded into contact with one another.

2. In the manufacture of variable high resistances comprising a high resistance surface, and

severed wire windings in Contact therewith, the method which includes cutting the wire windings by forcing a cutting edge simultaneously against all of the windings and at the same time indenting the ends severed thereby into the insulation core about which they are wound.

3. In the manufacture of variable high resistances comprising a high resistance surface, and severed wire windings in contact therewith, the method which includes winding the wire about a core, binding the wire windings permanently in position, and thereafter cutting the wire windings by forcing a relatively blunt cutting edge simultaneously against all of the windings in order to indent the or" the windings severed thereby into the insulation core about which they are wound.

4. In the manufacture of variable high resistances comprising a high resistance surface, severed wire windings in contact therewith, and a movable contact engaging said wire windings, the method which includes pressing the wire windings and resistance surface into intimate contact and simultaneously binding the wire wind ings permanent y in position, and thereafter cutting the wire wmdings by forcing a relatively blunt cutting edge simultaneously against all of the windings in order to cut them in parallel directions and to indent the ends of the windings severed thereby into the insulation core about which they are wound.

5. In the manufacture of variable high resistances comprising a high resistance element, a severed wire Wound element in contact therewith, and a movable contact engaging said wire wound element, the method which includes coating a thin insulation strip with resistance material and bending the same into arcuate configuration, winding an insulation strip with contact wire and bending the same into arcuate configuration, pressing the resistance and wire wound elements into intimate contact and simultaneously binding the wire windings in position, and thereafter cutting the wire windings along one edge of the insulation strip by forcing a relatively blunt cutting edge against the windings in order to indent the ends severed thereby into the insulation strip.

6. In the manufacture of variable high resistances comprising a high resistance element, a severed wire wound element in contact therewith, and a movable contact engaging said wire wound element, the method which includes coating an insulation surface with a high resistance material, winding an insulation core with contact wire so fine as will permit of a desired gradual resist ance variation and smoothness of operation but too fine to make the windings self-supporting in position when severed, pressing the wire wound and coated elements into intimate contact and simultaneously binding the wire windings in position and thereafter cutting the wire windings by forcing a relatively bunt cutting edge against the windings in order to indent the ends severed thereby into the insulation core.

'7. In the manufacture of variable high resistances comprising a high resistance element, a severed wire wound element in contact therewith, and a movable contact engaging said wire wound element, the method which includes winding an insulation strip with contact wire so fine as will permit of a desired gradual resistance variation and smoothness oi operation but too fine to make the windings self-supporting in position when severed, bending the same into arcuate configuration, binding the wire windings permanently in position, and cutting the wire windings along one edge of the insulation strip by forcing a tool having a relatively bunt arcuate cutting edge simultaneously against all of the windings in order to indent the severed ends of the windings into the insulation core.

8. In the manufacture of variable high resistances comprising a high resistance element, a severed wire wound element in contact therewith, and a movable contact engaging said wire wound element, the method which includes coating a thin insulation strip with resistance material and bending the same into arcuate configuration, winding an insulation strip with contact wire so fine as will permit of a desired gradual resistance variation and smoothness of operation but too fine to make the windings self-supporting in positon when severed, bending the same into arouate configuration, pressing the resistance and wire wound elements into intimate contact and simultaneously binding the wire windings in position, and cutting the wire windings along one edge of the insulation strip by forcing a relatively blunt cutting edge against the windings in order to indent the severed ends of the windings into the insulation core.

9. In the manufacture of variable high resistances comprising a high resistance surface, a severed wire-wound element held in contact therewith in a slot defined by side walls, and a movable contact engaging said wire windings, the method which includes winding an insulattion strip with contact wire so fine as will permit of a desired gradual resistance variation and smoothness of operation but too fine to make the winding self -supporting in position when severed,

coating an insulation strip with a high resistance material, pressing the thus prepared strips into the slot of the resistance element with a force fit in order to press the coated resistance surface and the adjacent side wall of the wire-wound surface into intimate contact and in order to tightly lock the fine wire convolutions firmly in place on both sides of the wire-wound strip, and only thereafter cutting the wire windings along an exposed edge.

10. In the manufacture of variable high resistances comprising a high resistance surface, a severed wire-wound element held in contact therewith in an annular slot defined by inner and outer cylindrical walls, and a movable contact engaging said wire windings, the method which includes winding a flexible insulation strip with contact wire so fine as will permit of a desired gradual resistance variation and smoothness of operation but too fine to make the winding self supporting in position when severed, coating a flexible insulation strip with a high resistance material, bending the coated strip and the wirewound strip into arcuate configuration, pressing the thus prepared strips into the annular slot of the resistance element with a force fit in order to press the coated resistance surface and the adjacent side Wall of the wire-wound surface into intimate contact and in order to tightly lock the fine wire convolutions firmly in place on both sides of the wire-wound strip, and only thereafter cutting the wire windings along the exposed arcuate edge by forcing a tool having a relatively blunt cutting edge against the windings in order to indent the severed ends oi the windings into the insulation strip.

LESTER L. JONES. 

